1. Field of the Invention
This invention relates to a lens barrel having optical members including a zooming lens, a focusing lens and a diagram.
2. Description of the Related Art
For the lens barrel of the kind arranged to move some of various lens groups with a stepping motor which is employed as a drive source by transmitting its driving force through the meshing engagement of a feeding screw and a rack screw, the stepping motor has been arranged to be approximately in a cylindrical shape for the purpose of imparting universal applicability to the stepping motor.
Further, a motor unit which is approximately cylindrical in appearance has been arranged as an actuator at a diaphragm driving part in cases where a linear movement is necessary, like in the case of the diaphragm driving part of a video camera.
However, the conventional arrangement mentioned above has presented various problems as described below.
An effort to minimize the size of a lens barrel without lowering its optical performance results in an approximately cylindrical shape of the lens barrel.
However, in order to arrange a driving part for each of a zooming lens, a focusing lens and a diaphragm to have a sufficient torque, the outside diameter of the lens barrel increases with a driving load. The increase in the driving load makes the driving part hardly containable within the shape of the minimum size of the lens barrel.
In the case of the conventional lens barrel which is shown in FIG. 6, an actuator unit 59 for driving a magnifying power varying system or a focusing system is formed with a U-shaped sheet metal member 59a arranged to support a motor 59b which is provided with a screw shaft 59c. The U-shaped sheet metal member 59a is screwed to the lens barrel 51. The lens barrel 51 has a cutout part 51a which is provided for mounting the actuator unit 59 thereon and extends over the whole moving range of the power varying system or the focusing system.
However, the structure of making the U-shaped sheet metal member 59a support the actuator unit 59 and of screwing the U-shaped sheet metal 59a to the lens barrel 51 necessitates the cutout part 51a of the lens barrel 51 to be large. The large cutout part 51a lowers the strength of the lens barrel 51 and also makes it difficult to attain a required degree of precision. The provision of the U-shaped sheet metal member 59a brings forth another problem which lies in that the meshing engagement of rack teeth (not shown) and the screw shaft 59c cannot be ascertained in their assembled state.
Further, for the lens barrel of this kind, use is generally made of a diaphragm unit including, in one unified body, a plurality of diaphragm blades, a diaphragm base plate and a blade retaining member which are arranged to sandwich the diaphragm blades therebetween, and a diaphragm driving part. The diaphragm unit which is arranged in this manner is disposed and fixed in position within the lens barrel in a state of being completely independent of the lens barrel.
However, the unitizing arrangement of the diaphragm device inevitably causes an increase in number of parts of the diaphragm device. The increased number of parts causes not only an increase in cost but also an increase in space required, and thus has resulted in a larger size of the lens barrel.
Further, depending on the mounting precision, the diaphragm unit tends to cause a discrepancy between an optical axis and the center of the diaphragm and thus has caused one of four corners of an image plane to become dark or, in the worst case, to be eclipsed.